Weak Immune System: Signs, Symptoms and Causes

Your immune system is something special. It’s constantly working to expel pathogens  — disease-causing organisms such as viruses, bacteria, fungi and parasites — from your body. 

It takes detailed notes, too, developing antibodies to protect you from pathogens it’s seen before. You can think of your immune system cells like soldiers in your personal army, constantly looking out for potential enemies.

It’s a big job, so it’s no wonder that sometimes your immune system loses a battle or two in the overall war to keep you healthy. 

How does your immune system work?

Your immune system provides two major kinds of protection: innate immunity and acquired, or adaptive, immunity. 

Innate immunity

You were born with an innate immune system, the organs, cells and proteins that work to recognize foreign organisms when they enter through your skin or digestive system. Sometimes this part of your defense system is called the “non-specific immune system”¹ because it uses the same tools — leukocytes, or white blood cells — to fight different threats.

Acquired immunity, aka adaptive immunity

Acquired or adaptive immunity is something you develop over time. When you’re exposed to a particular pathogen, either through illness or through vaccination, your adaptive immune system fights and studies it at the same time, producing specific antibodies it can use later if it tries to hurt you again. Since this system is constantly adapting, it’s best equipped to handle viral infections that change over time.²

What are the signs of a weak immune system?  

Constantly getting sick is a strong indicator that you may have a problem with your immune system. Typical signs can include: 

• Frequent colds, or a cold that lasts more than 10 days³
• Frequent viral or bacterial infections⁴
• Digestive problems like frequent diarrhea or constipation⁵
• Slow-healing wounds⁶
• Feeling tired all the time

What causes a weak immune system?

There are hundreds of potential causes of immune system weakness, but these are some of the most common:

Immune system disorders

According to Johns Hopkins Medicine, there are four main types of immune system disorders:⁷

• Primary immunodeficiencies: You’re born with an immune system disorder, which you probably inherited.⁸
• Acquired immune deficiencies: You develop a disease that weakens your immune system. This could be a temporary deficiency caused by the flu, certain drugs or medications or poor lifestyle habits, or it could be a long-lasting or permanent deficiency such as AIDS.⁹ 
• Overactive immune responses: Your immune army works too hard, treating harmless substances as threats. Allergic reactions to dust, plants and pet dander are examples of an overactive immune response.¹⁰ 
• Autoimmune disorders: Your system starts fighting your own body. It’s unclear why some people are prone to autoimmune diseases such as celiac disease,  diabetes and rheumatoid arthritis, but there is often a genetic link.¹¹

Lifestyle factors

Your habits and circumstances can affect your immune health. Some important lifestyle factors include: 

• Stress: Do you tend to get sick after an especially hectic week at work? Research shows that long-term stress can weaken immune responses.¹²
• Medications and other drugs: Certain medications, including chemotherapy drugs¹³ and steroids,¹⁴ can dampen immune health. So can drinking alcohol¹⁵ and smoking.¹⁶ 
• Sleep: Getting regular and sufficient sleep is associated with better immunity, while sleep deprivation can suppress the system.¹⁷‍
• Age: As we age, our immune defenses aren’t as quick to respond to new or previously encountered pathogens. This is a natural consequence of aging, so although you’re likely to get sick more often at 70 than at 20, it doesn’t necessarily signal an immunodeficiency.¹⁸ 
  

Can a doctor tell if you have a weak immune system?

Your healthcare provider can help diagnose immune problems. They may ask you about past illnesses or family history, or conduct a blood test to look at markers of immune health. There are also tests you can take at home to learn more about your immune system function.

How can you support your immune system?

If you’re feeling run down or just want to take extra precautions ahead of cold and flu season, there are several ways to support your body’s defenses. These include: 

• Minimizing stress: We know stress can weaken immunity, so anything you can do to avoid stressors can help.
• Getting enough sleep: For most adults, that means at least seven hours a night.¹⁹
• Staying up-to-date on all of your vaccinations: Vaccinations can teach your adaptive immune system how to defend itself.²⁰
• Practicing good hygiene: Washing your hands and avoiding touching your face can help prevent viruses such as colds and the flu.
• Drinking alcohol in moderation and abstaining from smoking: Minimizing or avoiding alcohol intake can reduce its immune-dampening effects,²¹ while quitting smoking is always a good idea.
• Exercising regularly: Regular exercise is associated with a range of health benefits, including stronger immune responses.²²
• Eating lots of fruits and vegetables: The food you eat matters, and malnutrition has been shown to inhibit the production of antibodies and immune cells.²³
  

Summary

Every person has an innate and acquired immune system, which can be weakened by disease, age and other lifestyle factors. You can boost your immune system by getting good sleep, eating healthy food and avoiding smoking and drinking alcohol.